Boolean is an abstract class defining the common protocol for logical
values. The logical values are represented by its two subclasses True and False.
There are no instances of Boolean in the system and there is only one
instance of True (which is the global true) and one of False (false).
Boolean redefines some messages which deal with copying Booleans,
to make certain there is only one instance of each.
The system will behave strange if you fiddle around here and create
new instances of True or False (i.e. it will not recognize these new
instances as being true or false).